There have heretofore been proposed a variety of deodorants and adsorbents capable of adsorbing offensively smelling components such as methyl mercaptans or volatile organic compounds (hereinafter “VOC”) such as formaldehydes and the like, usually, by using porous substances, such as active carbon, silica gel, zeolite, etc.
There have, further, been proposed various deodorants or adsorbents being added to thermoplastic resins which are molded into articles to impart thereto the performance for adsorbing the above components. For example, a patent document 1 described below is disclosing inorganic fillers such as active carbon, porous zeolite and sepiolite, or titanium oxide utilizing photo-catalytic action, which are capable of counteracting a wide range of smelling components and having heat resistance enabling themselves to be melt-mixed with the thermosetting resins.
There has, further, been proposed a deodorant using ultrafine metal particles, such as a deodorant using, as an effective component, a colloidal solution of ultrafine metal particles obtained by reducing, for example, a metal ion-containing solution (patent document 2).
However, the deodorants utilizing a porous substance exhibit their adsorption effect (deodorizing effect) upon adsorbing smelling components or VOC, and are accompanied by a problem in that their effect extinguishes if the adsorption sites are saturated. Further, in order to improve dispersion property, the inorganic filler must use a dispersant at the time when it is melt-kneaded with a thermoplastic resin. Therefore, there remains a problem in that the adsorption sites in the surfaces of the inorganic filler are covered with the resin or the dispersant causing the adsorption effect to decrease conspicuously.
Further, the deodorant utilizing the photo-catalytic action has a problem in that the surface of the titanium oxide must have been irradiated with ultraviolet rays at all times to decompose and deodorize the smelling components.
Moreover, if the deodorant containing ultrafine metal particles is added to the resin, then the resin is decomposed due to the ultrafine metal particles having a high surface activity, and the moldability is greatly impaired and, besides, a dispersion solution is necessary from the standpoint of handling. Therefore, the deodorant cannot be favorably added to the resin.
From the above points of view, the present inventors have attempted to make the organic acid component present on the surfaces of the ultrafine metal particles to decrease the direct contact between the metal surface and the resin, to effectively suppress the decomposition of the resin, and have thus proposed ultrafine adsorptive metal particles that suppress a decrease in the molecular weight of the resin and that do not impair the moldability (patent document 3).    Patent document 1: JP-A-9-75434    Patent document 2: JP-A-2006-109902    Patent document 3: WO2006/080319